Various types of systems have been used in the past to enhance switch opening and closure reliability. For example, it has been known to place switches in parallel to enhance circuit closing reliablity and to place switches in series in order to enhance circuit opening reliability. However, parallel switch arrangements degrade circuit opening reliability while series switch connection degrades circuit closing reliability.
Past prior art systems have generally utilized varying forms of redundant logic. For example, a plurality of redundant logic elements might be used, each having two output states. In such systems, the redundant logic output is often the majority output of the respective individual circuits. Alternatively, a primary path may be used and monitored to see if a defect has occurred. Upon detection of a defect, the element may be eliminated from the overall circuit and replaced with another element. These prior art redundant logic circuits were generally disadvantageous in that they included excessive elements which increased the chances of circuit failure.
It is therefore an object of the present invention to produce an electronic logic circuit for more reliable detection of switch openings and closures, even though one or more switches may fail to open and/or close.
It is another object of the present invention to utilize knowledge of past circuitry states to enhance reliability of such detection.
It is still another object of the present invention to produce an electronic circuit which monitors the output of redundant switches and simulates the connection of these switches in series during switch opening and parallel during switch closing to increase reliability during these respective states.
It is a further object of the present invention to perform the above-mentioned functions with a circuit having relatively few components and therefore exhibiting extremely high reliability so as not to detract from the otherwise enhanced reliability caused by use of redundant components.